Silver halide photography is superior to other photographic methods, such as electrophotography and diazo photography, in the photographic characteristics that can be achieved, such as sensitivity and tone control, and has, therefore, been used most widely. Recent years have witnessed development of technology for producing an image more easily and quickly by employing a heat-developing process, not relying on the use of a developer solution, in lieu of the conventional wet process which involves the use of developer and other solutions in the neighborhood of room temperature for the processing of a silver halide light-sensitive material.
The heat-developable light-sensitive material is known in this field of art and examples of such material and the process involved are described in the literature such as The Fundamentals of Photographic Engineering, pp. 553-555 Corona-Sha, (1979), Image Information, p. 40 (April, 1978); Neblette's Handbook of Photography and Reprography, 7th Ed., pp. 32-33 Van Nostrand Reinhold Company, (1977). U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777 and Research Disclosure pp. 9-15, (RD 17029) (June, 1978).
For the formation of color images by heat-development, a variety of processes have been proposed.
Regarding the formation of a color image through the coupling reaction between an oxidized developing agent and a coupler, U.S. Pat. No. 3,531,286 teaches the use of p-phenylenediamine type reducing agents and phenolic or active methylene type couplers; U.S. Pat. No. 3,761,270 describes p-aminophenol type reducing agents; Belgian Pat. No. 802,519 and Research Disclosure p. 31-32 (September, 1975) describe sulfonamidophenol type couplers; and U.S. Pat. No. 4,021,240 describes the combination of sulfonamidophenol type reducing agents with four-equivalent couplers.
Regarding the technology of forming a positive color image by the photosensitive silver dye bleach method, Research Disclosure pp. 30-32, (RD-14433) (April, 1976), Research Disclosure pp. 14-15, (RD-15227) (December, 1976), and U.S. Pat. No. 4,235,957, among others, describe useful dyes and bleaching methods.
The methods for forming an image by heat-development comprising the utilization of a compound having a built-in dye moiety and adapted to release a dye either in correspondence or in reverse correspondence with the reduction of silver halide to silver are described in European Laid-Open Patent No. 76,492 and No. 79,056 and Japanese Patent Application (OPI) Nos. 28928/83, 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Further, the methods for transferring the mobile dye imagewise formed by heat-development to an image receiving layer under heating and the associated image receiving materials are described in Japanese Patent Application (OPI) Nos. 58543/83, 79247/83 and 168439/84, for instance.
However, in these thermal image forming processes, as the necessary photographic reagents are not supplied from a developer solution or the like, all the photographic reagents required for development must be self-contained within the photographic light-sensitive material itself.
However, if the photographic reagents are added in their active forms to such a photographic light-sensitive material, they may react with the other substances contained in the light-sensitive material or be decomposed under the influences of heat, oxygen, and the like during storage before processing, with the result that they cannot be expected to fully display their designed functions.
One approach toward solving these problems involves blocking the active groups of photographic reagents and incorporating them in substantially inactive forms, namely as "precursors", in the photographic light-sensitive material.
When a photographically useful reagent in a dye, its functional group which would otherwise exert a material influence on its spectral absorption is blocked to shift the spectral absorption of the dye toward the short wavelength side of the long wavelength side. Then, if the dye is present in the same layer as the silver halide emulsion sensitive to the corresponding region of the spectrum, the loss of sensitivity due to the so-called filter effect can be obviated.
When the photographically useful reagent is an antifoggant or a development inhibitor, blocking its active group results in the suppression of its adsorption on the photosensitive silver halide and desensitization due to silver salt formation during storage, and as the photographic reagent is released at an appropriate time, it can be expected to obtain a fog without sacrificing the sensitivity, inhibition of fogging due to over-development, and termination of development at the appropriate time.
When the photographically useful reagent is a developing agent, a development auxiliary agent or a coupler, masking its active group or adsorbent group enables prevention of photographically undesirable influences due to formation of a semiquinone or oxide and prevents generation of fog nuclei during storage through prevention of the influx of electrons into silver halide, thus contributing to stable processing.
When the photographically useful reagent is a bleaching accelerator or a bleach-fix accelerator, too, blocking its active group leads to the advantage that the reaction thereof with other concomitant substances is inhibited during storage while the expected function of the reagent may be deployed to advantage by unblocking during processing.
Regarding such technology for blocking photographically useful reagents, several specific procedures are known in the field of conventional photographic light-sensitive materials. For example, the prior art includes the use of acyl or sulfonyl groups as a blocking or masking group as described in Japanese Patent Publication No. 44,805/72, the use of blocking groups such that photographically useful groups are released by the so-called reverse Michael reaction as taught in Japanese Patent Publication Nos. 17369/79, 9696/80 and 34927/80, the use of a blocking group such that a photographic reagent is released in timed relation with the formation of a quinonemethide or quinonemethide-like compound through intramolecular electron transfer as described in Japanese Patent Publication No. 39727/79, Japanese Patent Application (OPI) Nos. 135944/82, 135945/82 and 136640/82, the utilization of an intramolecular cyclization reaction as described in Japanese Patent Application (OPI) No. 53330/80, and the use of a ring-opening reaction of a 5-membered or 6-membered ring system as described in Japanese Patent Application (OPI) Nos. 76541/82, 135949/82 and 179842/82.
However, these known techniques invariably utilize hydrolysis or deprotonation due to the action of OH.sup.- in wet development at or near room temperature and useful precursor technology has not been known in the field of heat development (also referred to as thermal development) using an organic base.